Power amplifiers are widely used in wireless communication systems and other electronic devices, especially in mobile devices. To achieve high system efficiency and/or longer battery life, it is very important to maintain high efficiency in power amplifiers.
The power amplifiers in many systems see signals with high peak to average power ratio. Because a typical power amplifier gets its energy from a power supply coupled to the drain (or the collector if a transistor is used) of its main power switch (a MOSFET or a transistor), its power efficiency can be improved by changing the drain voltage of its main power switch through changing the voltage of its drain power supply according to the envelope of the signal being processed by the power amplifier. When the signal envelope has high bandwidth as often seen in today's wireless systems, changing the voltage of drain power supply may cause the output signal of the power amplifier to be distorted.
Moreover, as the bandwidth of the signal increases, the power supply's control bandwidth should be increased accordingly. This put very high burden into the power supply, and the efficiency of the power supply is low with existing technology.
Improvements are needed to reduce the signal distortion in a power amplifier with variable drain voltage, and to increase the efficiency of the drain power supply.